Update commentary to use Ax%sT format where appropriate.

* Theory, tz-link.htm: Replace formerly-ambiguous EST in North America
and Australia with still-ambiguous CST in North America and China as
the anecdote used to caution against reliance on abbreviations.
* asia, australasia: Update commentary on abbreviations in use.
* zic.8: Update example Zone line (Australia/Adelaide) to use AC%sT
instead of CST.